He has bilateral Duane’s retraction syndrome, with the tell-tale pseudo-ptosis from ocular retraction during adduction. Duane syndrome is an anomalous innervation of the lateral rectus by fibres destined for the medial rectus. The abducens nerve itself is absent and its nucleus hypoplastic or absent too. Hence it is a congenital maldevelopment, which explains the lack of diplopia.

Duane’s syndrome is a relatively common congenital ocular motor anomaly, accounting for about 1-4% of patients in strabismus clinics. However, this patient also has another interesting anomaly: contralateral deviation of the jaw with lateral gaze to either side. This would be consistent with activation of the ipsilateral lateral pterygoid with attempted abduction. This is an abducens-trigeminal synkinesis, a much rarer but similar aberrant innervation pattern. It is reminiscent of the more well-known Marcus-Gunn jaw-winking phenomenon, which is a trigeminal oculomotor synkinesis, in which jaw movement causes lid elevation.

Trigeminal-abducens synkinesis, with ocular abduction provoked by jaw movement, can occur in both congenital (Kodsi, 2000; Ghodasra et al, 2009) and post-traumatic (McGovern et al, 1986; Nelson and Kline, 1990; Krzizok and Graf, 1994; Park and Oh, 2013) forms. Abducens-trigeminal synkinseis may be rarer, but again with examples of congenital (Lai et al, 2003) and post-traumatic forms (Shulman et al, 1998). A case similar to ours, with associated Duane’s syndrome, has been described (Emre and Henn, 1987).

When acquired, it has been postulated that the point of aberrant innervation may occur in the cavernous sinus, where the V3 and VI nerves are close to each other.